The present invention relates to apparatus and methods for precisely detecting the position of a moving object carried by a robot as an aid to the precise transfer of that object and, in particular, to apparatus and methods for precisely determining the position of a moving integrated circuit wafer on a robot arm relative to a storage elevator.
FIGS. 1 and 2 depict a multiple chamber wafer fabrication system 10, which is described in greater detail in the Detailed Description. In system 10, wafers 15 are transported on blade 31 of robot 30 between an external cassette elevator 18 and an internal loadlock storage elevator 19, between the internal elevator 19 and one or more (preferably a multiplicity of) processing chambers 12, and between the chambers. This system is compact and presents precise tolerance requirements, for example, for loading the internal loadlock storage cassette 19 from the external elevator 18. As a consequence of the tight tolerances and the resulting need to precisely insert each wafer 15 into the internal loadlock storage cassette 19, the position of each wafer must be precisely determined relative to the robot blade 31 after the wafer is unloaded from the external cassette elevator 18. This determination is complicated by the movement of the wafer 15 and, specifically, by the operational preference for determining the position of the wafer without interrupting movement of the robot and wafer.